Extraction process



May 25,A 1937. w. J. D; vAN DUCK 2,081,720

EXTRACTION PROCES S Filed om. 19, 195s Improved Primary 7 $77.] H92 uH93' Patented May 25, l 1937 UNITED sTATEs wiuem J. n. van Dijck, TheHague, Netherlands, assignor to Shell Development Company, SanFrancisco, Calif., a corporation of Delaware Application October 19,1933, Serial No. 694,280 In the Netherlands November 18, 1930 Bussum sinatA 23 claims. (C1. 19t-1a) This invention relates to extractionprocesses and constitutes an improvement thereof directed to increasethe yield and improve the purity of substances or groups of substanceswhich are obtainable by extraction of liquid mixtures containing thesame. The'present application is a continuation in part of theapplication Serial No. 567,970 filed October 9, 1931.

While extraction processes for separating components of liquid mixtureswere known for a long time, the degree of separation as represented bythe yield and/or purity of the obtained products, was ordinarilyconsidered to be limited by the dissolving capacity and theselectivity-fof thesolvent at the most favorable uniform operating'temperature. As an advancement in the extractingart, the principle ofcont-inuous countercurrent operation is now being widely applied.

More recently it was proposed to extract liquid mixtures by means l,oftwo partially miscible solvents, flowingcountercurrently to and incontact with each other and through the mixture being extracted, wherebythe components soluble in the corresponding solvents are separated fromthe mixture It was also' prcposedxto substitute one of such selectivesolvents by one of the components previously separated from the mixture.

It is known further to operate the extraction processes so that theextract and raflinate phases are separately removed from an extractionzone or column and chilled. As a result each of theseprimary phases iscaused to separate into secondary extract and raffinate phases outsideof the extraction zone, and the secondary rainate phase chilled out ofthe primary extract phase is returned to the zone at a point near theenter-l ing fresh feed and is mixed therewith, while the secondaryextract phase, chilled out of the primary raflinate phase, is returnedto the main column at a point near the entering fresh solvent; thesecondary extract and raiiinate phases not returned tothe column arefreed of solvent. The purpose of such chillingis to obtain a betterextract and a better rafiinate than those which would be obtained fromthe extraction zone at a normal or elevated temperature. effect may beproduced by chilling either or both ends of an extraction zone or columnjust beyond the points of entrance of the feed and the solvent. Thisprocess is described in the German Patent No. 410,169. The particularfeatureof the process of this type is that the composition of thesecondary extract phase separated from the primary one by cooling willremain constant,

The same,

as it is fixed only by compOsition of the intake, the relative quantityof solvent and the temperature of cooling.

As an' improvement ofthe above outlined extraction processes, -thepresent invention contemplates among other features a countercurrentwashing of the primary extract phase produced in an extraction zone witha secondary railinate phase chilled out of a primary extractl phaseobtained in an earlier operation of the process. As a result .of thiswashing the composition of the ultimate extract phase produced in theprocess can be conveniently regulated and improved in the manner and tothe degree unobtainable in the old processes which did not employ thiswashing step.

In the description of the process of this linvention the followingnomenclature will be employed:

A and B are components of the mixture to be extracted.

'I'he term component" applies to a portion of a mixture to be extracted,which portionis distiiict from other portion or portions of the samemixture in its chemical and/or physical properties, in that it can beeither partly or completely The terms solvent or uselective solventapply to va preferential solvent for B when both components are broughtinto contact with said solvent; it may have either lower or higherspecic gravity than that of the A+B mixture, and may be either partly ortotally miscible with B at the extraction temperature.

The term auxiliary solvent applies to either a non-selective solvent ora preferential solvent for A used in conjunction with the selectivesolvent; preferably it should be only -partly soluble, if at all, in theselective solvent.

The terms primary ramnate phase and primary extract phase apply to theliquid phases (with relatively low and high contents of the solventsrespectively) obtainable'a from the extraction zone, or a column.

The term secondary raiiinate phase applies to the rafiinate phaseseparated from an extract phase by cooling .or by wholly or partiallyevaporating the solvent from the extract phase and contingently coolingthe remainder. Its solvent content is always lower than that of theoriginal extract phase.

lseparated from said'mixture in a more or less pure state by solventextraction.

, The term secondary extract phase" lapplies to f the extract phaseremaining when the secondary rainate phase has been removed from anextract phase e. g. by cooling.

The termsrainate and "extract apply to the solvent-free portions of therespective phases.

The term improved or better extract applies to an extract with acomparatively greater concentration of B.

The term improved or better raffinate applies to a raffinate with acomparatively greater concentration of A.

'Ihe term improved or better extract phase applies to an extract phasecontaining an improved extract.

The term improved or better raffinate phase applies to aranate phasecontaining an improved raflinate.

The'term extraction column applies to a single extraction column or aseries of intercontion of the extraction column between the entrance ofthe selective solvent and that of the mixture being extracted.

The term washing zone applies to a zone having a substantial lengththrough which the primary extract phase is to 110W under conditions ofthis invention. The washing zone is adjacent and below the feed when arelatively heavy solvent is used, and above the feed when a relativelylight solvent is used. The feed is introduced between the extraction andwashing zones.

It is an object of this invention to provide an extraction processwhereby the composition and /or yield of a secondary extract may beimproved at will without resorting to the employment of a chillingprocess only as would` be necessary for producing an analogous, improvedextract by old methods using one solvent.

Briey, the inventionresidesin the discovery that when a stream of theprimary extract phase is allowedto flow down from the feed level, as itwould be, for example, in the case of employing a relatively heavysolvent, through a washing zone of a substantial length, at the end ofwhich zone for example this stream. is chilled, to a. suitabletemperature, so that a, secondary railinate'phase and a secondaryIextract phase are formed, this secondary rafnate phase, which is thusricher in B than a raffinate phase in equilibrium with the primaryextract phase at the elevated temperature, being allowed to rise throughand mix (contact) over a substantial length with the descending streamof the primary extract phase within said washing zone and below and awayfrom the incoming feed, then, as a result of this contacting, thecompositions of both these phases change, so that an improved primaryextract phase would reach the chilled part of the zone and followingthis an improved secondary extract phase will separate from the chilledmixture. 'I'he new secondary raiiinate phase to be returned to thewashing zone, which will be in equilibrium with the improved secondaryextract, will bevstill richer in B, and will enrich still more thedescending stream-o1" the gradually improving -primary extract phasewith the component B.

The rising cold secondary raflinate phase formed upon chilling theprimary extract phase will meet a stream of the primary extract whichcomes from a hotter region. The result will be a change in temperatureof both phases, which will cause anexchange of components between ythetwo phases, as at'the changed temperature the solubility relations havechanged also.

It may be, however, that the temperature of the descending stream is sohigh, that when the two phases in question meet at a certain point ofthe washing zone, owing to the exchange of heat the temperature of themixture becomes so high that a complete miscibility of the two phasespresent at the point under-discussion occurs. If however two phasescannot exist next to each other, no washing can be carried out.

been found that this feature will prevent complete miscibility of thetwo phases at any point of the washing zone.

This temperature gradient may be created by cooling down the primaryextract phase so far that the secondary raiiinate phase formeithere.- byis so cool that when it rises its temperature vis graduallychanged bycontact with the downcoming warm stream of the primary extract phase,andthe temperature Within the washing zone is caused to be so low thatvthere never occurs a complete dissolution of the phases.

As, however, the cooling of the primary extract phasealso causes acertain amount of secondary raiiinate to be formed, it is evident thatthese two magnitudes, i. e. the amount of the secondary It is thereforeadvantageous to control the temperature throughout the washing zone atthe place Where this has to be done e. g. by outward means, such ascooling jackets, so that it is not necessary to rely upon the effectcreated by the cooled secondary rainate alone.

From the above it is observed that by the continuous chilling of theprimary extract phase at the end of the washing zone and by continuouslyreturning the secondary raffinate phase to said zone to rise through andcontact with the primary extract phase, thereby taking care that as faras possible a gradual change in temperature is maintained throughout thewashing zone, the

composition of the secondary extract phase will be improved, so that byregulating the amounts of the feed (A+B) and the solvent, whilemainasimilar view of the column adapted for carr,v ing out theextraction process hereafter speciiicallyv described.

Fig. 1 of the drawing represents a vertical extraction column providedwith pipeconnections I, 2,- 3 and 4, for introducing the feed and thesolvent, and forwithdrawing `the raiiinate and extract phases,respectively. The extraction column ,communicates with a cooler 5through the pipes 4 and 5, the latter being provided with a pump, ifnecessary, for conducting a liquid from the top of4 the cooler to apoint of the column,

maintain the contents of the cooler at a tempera- I ture below that ofthebottom part of the column.

In practice, the length f the extraction zone of the column, i. e. itsupper part, or the number of mixing and settling stages in theextraction zone, is so selected as to insure the desired composition ofthe raiiinate phase at the top Aof the column, while the feed A+B isintroduced at or near the level of the column where the rafilnate phasewhich is rising through the column and is undergoing extraction containsa raffinate of substan-l tially the same composition as the feed. Thelower part between pipes l and 5 must be of a substantial length inorder to provide for proper countercurrent contact between secondaryrailinate phase and primary extract phase and to cause the compositionof the secondary ramnate to approach the ycomposition of the feed, andbelow pipe 5 for 'settling out -of the improved primary extract phase tobe withdrawn into the cooler 5.- y

In-the operation of this, extraction apparatus, when the feed and thesolvent are supplied to the column through their respective pipeconnections,

v two streams of phases are formed within the extraction zone of thecolumn. The raiiinate phase is collected at the top and withdrawnthrough the pipe 3, while the extract phase, i. e. the phase withgreaterl solvent content, settles down and tends to collect below thefeed pipe I. 'I'his extract phase is withdrawn from the column throughthe pipe 4 into thecooler 5, where itis chilled and caused to separateinto secondary ramnate and secondary extract phases; these are allowedto settle out and are withdrawn from the cooler throughpipes 6 and 1,respectively.

The secondary raffinate phase is returned to the column through the pipe6 and contacted 'with the descending primary extract phase, with theresult that an improved primary extract phase is withdrawn through thepipe 4. `A further improved secondary extract phase is separated in thecooler and withdrawn therefrom. As the operation'l is continued, theprocess of improving the composition of the secondary extractphaseprogresses, tending to reach certain limits fixed by the operatingand solubility conditions within the system, with the result that anextract rich in B and poor in or often even substantially free of A canbe obtained. It may be found desirable especially in case of somesolvents, in order to increase the efficiency of separating the mixtureA+B into its components to regulate the temperature gradient from thetop to the bottom of the column, that the upper part thereof would beoperated at relatively elevated temperatures, while the lower part wouldbe cooled to relatively low temperatures (when a relatively heavysolvent is used; viceversa in case of a light solvent)v all thetemperatures being determined by solubility characteristics of thecomponents and the solvent and their relative proportions at each levelwithin the entire column. If desired, the processmay be modifiedanalogous to the manner of operation of the lower section of thecolumn..

y The ultimate extract phase. as well as the ramnate -phasefrom the topof theextraction column, after being withdrawn from the extractionprocess, are separately treated to separate the extracty and theraflinate, respectively, fro'm the solvent.

An essential feature of the process illustrated by Fig. 1 is thereintroduction of the secondary rallnate phase through the pipe 6 intothe main column at a point so remote from the feed pipe l that 4thissecondary rainate phase upon being introduced into the column and owingto the fact that a' temperature gradient is maintained, would so changeits compositionwhile rising to the level of the feed, that itssolvent-'free portion at that level would approach as nearly asvpossible the composition of the feed. The extract phase separating nearand below the level of the pipe 6 will then be an improvedy primaryvextract phase, formed principally not by lowering of the temperature atthat part of the column, ,but as a result of the countercurrent washingof the primary extract phasewith the secondary rafnate phase. It followsthen, that the distance between the entrance of the feed and that of thesecondary rainate phase, i. e. the washing zone', should be of anappreciable length, which is to be referred to as an effective length ordistance This length may be different for different solvents andmixtures to'be extracted and is a function of 'various properties suchas their gravities, viscosities and solubility characteristics atextraction temperatures. Similar conditions should prevail in the lowerwashing zone of the cooler 5 when the cooler 5' is used, as described.

To point out more clearly the difference between thenew process and suchold methods as the ones described in the German patent, it will be notedthat in accordancefwiththat old method the secondary raffinate phaseshould be returned byv means of pipe l5 (broken line of Fig. 1) nearthellevel of the pipe I. I Such method, while pro- .ducing a secondaryextract phase of a better composition than the primary extract phase,will not operate in such ,a manner as progressively to improve saidcomposition, but would produce a proved by providing an additionalcooling means 9 intermediate the feed and the entrance of the secondaryraihnate phase. l

' From the foregoing explanation it would follow that the step-wiseprocess of Fig. 1 can be carried out in the manner illustrated vby Fig.2, which represents an' extraction column provided with pipe connectionsl, 2, 3 and 1 for introducing the mixture tobe extracted and a solventand withdrawing the railina'te and extract phases', respectively. Acoolingmeans, such as a cooling coil 8, is provided at the lower sectionof the column, forming a chilling zone ,and a washing zone of aneffective length. Cooling means 9 and l0 may bei' provided along thewashing zone in order to maintain a gradual temperature drop from thelevel of the feed towards the chilling zone. A settling l zone,insulated by means I4, if desired, 'may be provided at the bottom of thecolumn.

The operation of the process of this type is dif- .drawing the separatedphases.

ferent from'the process as shown in Fig. 1 only in that the washing ofthe descending extract phase below the feed is gradual throughout thewashing zone of an effective length, i. e. is not step-wise as shown inFig. 1, while the principle involved and the result are the same, thatis the ultimate extract phase withdrawn through pipe 'l is much betterthan the extract phase, which it would be possible to obtain bywithdrawing the extract phase immediately below the feed and chilling itto the same temperature as is had near the coil 8, even if the secondaryrafllnate phase in this case would be returned to the column near thefeed level. v

It was also found that the eiliciency ofv separating components A and Bfrom their mixture by extraction with a solvent can be increased, if theoil content of the downward streamV of the extract phase within thecolumn is maintained substantially constant. To accomplish this, heatingmeans Il, i2 and I3 may be provided to maintain a gradually decreasingtemperature within the extraction zone in the direc.

restricted to the use of preferential solvents heavier than the mixtureto be separated, as the preferential solvent may have a lower speciegravity than the mixture to be extracted, in which case the extractphase of the mixture is caused also to pass `through regions ofgradually and effectively lowering temperature, so that thelowesttemperature. prevails at the part of the extraction zone near the pointwhere the extract phase is being collected and withdrawn, (top of theextraction column, for example) while a relatively higher temperature ismaintained at the part of the zone, near which the raffinate phase isremoved (bottom of the extraction column, for example). v -e The processmay be further explained by the following example illustrated by Fig. 3diagrammatically representing in cross-section another formh of theextraction apparatus -which was used inI carrying out the extractionhereafter described. The extraction column was provided near one endwith a solvent inlet pipe 2 and with an oil feed pipe l near the middleof the column.` Ateach end -of the column draw off pipe connections 3and 4 were provided for with- One of these pipe connections, namely,theextract phase draw off line, was connected to a cooler 5, providedwith a coil 8 and pipe connections 6 and 1. The cold secondary ramnatephase produced by cooling was withdrawn from the bottom' of the cooler 5through the ypipe connection 6 and was then returned to the' extractioncolumn entering the column near the end from which the extract phase.was being withdrawn.

The continuousprocess, as carried out in this apparatus consisted ofintroducing a stream of lubricating oil to be extracted into'the columnthrough the pipe I and feeding. at the same time @d/0 alcohol throughthe-pipe 2. Due to the lower specific gravity of the alcohol as comparedto that vof the oil, and due` to .the fact that the oil and the alcoholare not miscible i phase.

with each other, but form, on being contacted beyond certain knownproportion limits, two phases, such phases were formed and withdrawn atthe respective ends of the column. The ramnate phase descended throughthe extraction zone towards the incoming alcohol and was withdrawnthrough the pipe 3, while the extract phase was withdrawn at the top tothe cooler 5, where it was chilled. The separated secondary ralnatephase was withdrawn by means of pipe 1 and the raffinate phase wasreturned to the column by the pipe 6. The temperatures within the columnwere maintained as follows: 120 C. at the top, 140 C. near the entranceof the lubricating oil and 150 C. at the bottom of the column. A highly-naphthenic extract was obtained. 'I'he described process was carriedunder Y superatmospheric pressure in order to eliminate the formation ofvapors.

dIt is obvious that the above extraction could be carried out byeliminating the cooler and providing, instead a chilling zone near thetop of the column, by placing a cooling means in that part of thecolumn, thereby forming a phase by withdrawing the primary extract phasefrom the column at the end of its travel through the washing zone. Thereare several methods of producing from this liquid the secondary ramnatephase necessary to carry out the countercurrept washing processthroughout the washing of the process of the invention.

Bearing in mind that the secondary rafiinate phase must be co-existentwith the primary extract phase at the point where this secondaryraflin'ate phase is introduced into the washing zone and atv thetemperature prevailing there. it may be that the primary extract phasewithdrawn from the column only consists of a saturated solution of thepure component B in the selective solvent. In order to make sure thatthis solution always contains only B it must be continuously inequilibrium with a phase containing only B and no A. It may contain somesolvent, but this is not necessary, for a liquid consisting practicallyentirely of Bl can be in equilibrium with a saturated solution of B inth solvent. y i

In order to prepare such an equilibrium solution it is thereforepossibleY to evaporate partly or wholly the solvent from the primaryextract phase of the above assumed character, and to use a part of thissolution as secondary extract Attention may be drawn to the fact thatwhen the whole` of the solvent is evaporated there is no difference incomposition between the secondary extract and the secondary raflinatephase.

The method of partially or wholly evaporating the solvent from theprimary extract withdrawn from the column and using a part of the liquid'obtained as vsecondary raflinate phase, is also applicable when no purecomponent B is made Vas extract.

to be subsequently cooled to a suitable temperav ture, so that itseparates into a secondary rainate and an extract phase, and the cooledsecondary taining a gradual temperature drop within the rannate phase,i. e. tnt with .the low solvent mixture of the two iiowing phases in thedireccontent, to be returned to the washing zone of the column at aneilective distance from the feed.

the above methods is co-existent with the primary extract phase at thetemperature at which it is introduced, it will act as a washing agentvsus amylacetate and others.

when at another level it is contacted at a higher temperature with theprimary extract phase, travelling countercurrently.

Comparing the processwith that in which a y liquid mixture is extractedwith-two non-misciblev solvents flowing in countercurrent to each other,it may be said that whereas in the iirst process two phases created bytwo solvents travelling present process it is not necessary that twosolvents travel throughout the whole column, it being only necessary tomaintain two phases.

One of these phases comprises the preferential solvent laden withcomponents, whereas the se'cond phase ilowing in countercurrent theretoconf tains no auxiliary solvent flowing through the whole column and isnot laden with `components but has a changing composition, a temperaturegradient being necessary to prevent this second phase from disappearingas phase in a certain part of the column.

It goes without saying that a process as described in the presentspecification can be repeated several times both with the secondaryextract and the railinate obtained with the combined extraction andwashing processes. Each of the products of this first combined -processis then extracted and washed separately with a solvent, either the sameas that used inl the ilrst combined process or another solvent. inecessary to carry out all these processes at the same temperature orwithin the same temperature range.

Such a process is specially recommendable when the initial productconsists of various series of products, the members of which possessproperties which are mutually not widely divergent. The rstextracting-agent can then, for example, be used to separate the groups-of homologues, whereas with a more selectively acting and often muchmore expensive extracting-agent the op-. eration is continued with asmaller quantity of initial product, whlchpresents the advantage ofsmaller quantities being required of the second auxiliary liquid.

'I'he method of this invention may be applied to extractions ofdifferent kindsof liquids,.such as hydrocarbon oils, e. g., mineral oilsand their distillates, tars or to the extraction oifatty acids such asacetic acilgfromtheir aqueous solutions with various selective solvents,such as .liquid SO2, furfural, isopropyl alcohol, aniline, nitrobenzene,chlorex, phenols, organic nitriles and thiocyanates, ketones, aldehydes,esters such as It may also be used in two-solvent extractions, whereinone of the solvents is a selective solvent, while the other is anauxiliary solvent; in this case the operation of the method, asdescribed for a-single-solvent extraction, would be the same as if onlythe selective solvent were used.

I claim as my invention:

1. In a countercurrentA process for extracting a liquid mixture ofhydrocarbons wherein a raffinate phase-flows in contact with andcountercurrently to an.A extract phase thestep of mains If the secondaryramnate phase `formed byv yent and the mixture into the apparatus,separately withdrawing said phases therefrom, re-

It -is not.

- tus and the mixt washed extract phase to separate from it la. solute15,

phase, and using vthe separated vsolute-phase as Vthe washing liquid.

3. In an extraction process carried out by means of an extractionapparatus having'extraction and washing .zones andprovided with meansfor introducing a solvent and a mixture to be extracted, and means forwithdrawing the ultimate rainate and extract phases produced by theprocess,A the steps of introducingthesolmoving the solvent from thewithdrawn extract phase, returning a part ofthe extract into theAapparatus at an eective ldistance from the entrance of the mixture andsubjecting the liquids owing through the washing zone to a thermaltreatment to create a gradual temperature drop in the direction of ilowof the extract phase.

4.1In an extraction process carried out by means of an extractionapparatus having extraction and washing zones and provided with meansforintroducing a solvent and a mixture to be extracted, and means forwithdrawing the ultimate raffinate and extract phases produced by theprocess, the steps of introducing the apparae into thecolumn, separatelywithdrawing sai phases therefrom, removing from the withdrawn extractphase a portion ofthe solvent, cooling the remaining portion of thephase, thereby causing its. separation into secondary raiilnate andextract phases, separating the two cooled secondary phases and returnlngthe cooledsecondary rainate phase into the 'apparatus at an eiectivedistance from the enstep of regulating the heat content of the ilowingphases so as to cause a gradual temperature drop inthe direction of ilowof the extract phase.

6. In a. process of fractionating a liquid mixture of components bycountercurrently contact-` ing a iow of the mixture with a -ow of apref-- erential solvent so asgto produce a flow of a solution of solublecomponents of lthe mixture in the preferential solvent, the step ofcontinuing the flow of said solution after the solvent h as been.contacted with the liquid mixture and subjecting said continued f lowto a change in temperanow, of a preferential solvent, the step. of.sube. 75' i jecting the flow of thel solvent after it has taken up aquantity of the liquid mixturev soluble in the-so1vent to a change intemperature over a substantial length of the continued flow of thesolvent after the latter has been contacted with the liquid mixture,said change in temperature being provided in such a way that thetemperature decreases in the direction of flow of the solvent andrecovering a solution of the dissolvedcomponents in the preferentialsolvent at the end of its continued flow and the undissolved componentsof the liquid mixture at the end of the now of the liquid mixture. l

8. The process of separating a mixture of liquid components into twocomponents, which comprises introducing a ow-of said mixture into acolumn at a point between the top and the bottom thereof, contactingsaid mixture in said column with a countercurrent flow of a preferentialliquid solvent and maintaining as far as possible a gradual change intemperature throughout at least a substantial length of that part of thecolumn which is situated past the point of entrance of the mixture ofliquid components in the direction of flow of the preferential solvent,the gradual change of temperature being such thatthe'temperaturedecreases in the direction of flow of the preferential solvent andrecovering the less soluble component at a point past the point ofentrance of the mixture in the direction ofthe now of said mixture andthe morey soluble component dissolved in the preferential solvent at a.point past the point of entrance of said mixture in the direction offlow of the preferential solvent.

9. 'I'he process of claim 23, wherein the mixture to beextractedisintroduced into'the apparatus at a point where thesolvent-free portion of the rafiinate phase lhas substantially the samecomposition as that of the mixture.

. 10. The process of claim 23,.wherein the contents of the apparatuswithin the Washing zone are in addition progressively cooled throughoutsaid effective distance.

11. The process of claim 23, wherein a gradual temperature gradient ismaintained throughout the extraction apparatus whereby the molalquantity of the solvent free,portion of the ex- A tract phase ismaintained constant throughout the column.

l2. In an extraction process carried out by means of an extractionapparatus having extraction and washing zones and provided with .meansfor introducing a solvent and a mixture to be extracted, and means Aforwithdrawing the ultimate rainate and extract phases produced by theprocess, the steps of introducing thel solvent and the mixture into theapparatus, separately withdrawing said phases therefrom, ysubjecting thewithdrawn extract phase to cooling, thereby producing a secondaryraffinate phase and a new extract phase, separating these two phases andreturning the cooled secondary raillnate phase into the apparatus at' aneffective distance from the entrance of the mixture.

13. The process of separating a mixture of liquid components into saidcomponents, which comprises contacting the mixture of liquid componentswith a. preferential liquid solvent while the mixture of liquidcomponents and the'preferential solvent are flowing countercurrentlywith respectI to each other in separate liquid phases in the samegenerally conned and elongated column of liquid comprising the saidpreferential solvent and the liquid components to be sepaaccingo rated,and maintaining as far as possible a gradually changing temperaturethroughout the greater portion of the length of the said column ofliquid, which temperature decreases in the direction of flow of the saidpreferential solvent, thus causing some of the more soluble component tobe separated out of the said solvent in the said gradually increasinglycooler environment whereupon the liberated more soluble componentdissolves the less soluble component present in and moving out of thepreferential solvent and flows countercurrently to the said preferentialsolvent, causing the more soluble component to be gradually redissolvedby the said preferential solvent, and finally recovering the lesssoluble component and the more soluble component dissolved in the saidpreferential solvent at opposite ends of the said column of liquid.

14. 'I'he process of separating a mixture of liquid components into saidcomponents, which comprises contacting the mixtureof liquid componentswith a preferential liquid solvent while the mixture of liquidcomponents and the preferential solvent are flowing countercurrentlywith respect to each other in separate liquid phases, the preferentialsolvent having a greater specific gravity than themixture of liquidcomponents, whereby the said preferential solvent will flow downwardlyin the same generally confined and elongated column of liquid comprisingthe said preferential solvent and the liquid components to be separated,and maintaining as far as possible a gradually changing temperaturethroughout the greater portion of the length of the said column ofliquid, which temperature decreases in the direction of flow ofthe saidpreferential solvent, thus causing some of the more soluble component tobe separated out of the said solvent inthe said gradually increasinglycooler environment, whereupon the` liberated more soluble componentdissolves the less soluble component present in and moving out of thepreferential solvent and flows countercurrently to the said preferentialsolvent, causing vthe more soluble component to be gradually redissolvedby the said preferential solvent, and

nally recovering the less soluble component and the more solublecomponent dissolved in the said preferential solvent at opposite ends ofthe said column of liquid.

15. In the process of extracting a liquid mixture of components in anextraction zone with a selective solvent for one of said components toproduce an extract phase and a raflinate phase having different specificgravities, the improvement which comprises the steps of withdrawing theextract phase from the extraction zone, flowing it through a washingzone in countercurrent to a washing liquid subsequently described toproduce a phase which hasy alow solvent content and a washed extractphase, maintaining a gradual temperature drop in the washing zone in thedirection of flow of the extract phase, the temperature of the extract'phase after it has traversed at least a substantial portion of thelength of the Washing zone being low enough to cause a solute phase toseparate from it, and using the separated solute phase as the washingliquid.

16. In the process of extracting a liquid mixture of hydrocarboncomponents in an extraction zone with a selective solvent for one ofsaid components to produce an extract phase and a ranate phase havingdifferent specific gravities, the

prises the steps of withdrawing the washed extract phase from thewashing zone, chilling it to separate it intoa solvent phase and asolute phase,

- separating said phases, and returning at least a portion of the solutephase to the washing zone as the washing liquid.

18. A process according to claim 2 in which the extract phase is chilledto separate out a solute phase while it is within the washing zone.

19. The process according to claim 2 which comprises the steps ofremoving at least `some of the solvent from the washed and chilledextract phase and returning a portion of the resulting solvent-poorextract phase to the washing zone as a component of the washing liquid.

20. In the process of extracting a liquid mixture of components in anextraction zone with a selective solvent for one of said components toproduce an extract phase and a raffinate phase vhaving different specicgravities, the improvement which comprises the steps of withdrawing theextract phase from the extraction zone, flowing it through a washingzone in countercurrent to a washing liquid subsequently described tovproduce a phase which has a low solvent content and a washedextractphase, maintaining a gradual temperature drop in the washing zonein the direction of ow of the extract phase, withdrawing the washedextract phase from the washing zone, removing at least some of thesolvent from the washed extract phase, and returning a portion of theresulting solvent-poor extract phase to the washing zone as the Washingliquid.

21. In the process of extracting a mineral oil with a liquid solventwherein some of theoil components are more readily soluble than otheroil components the step ofvcommingling the oil and the solvent underconditions to form a primary extract phase and a primary raflnate phase,separating the phases, flowing the primary extract phase through awashing zone countercurrently and in contact with a washing liquidsubsequently described to produce a phase which has a low solventcontent and a washed extract phase, chilling the washed extract phase toseparate from it a secondary rafflnate phase and using the separatedsecondary railnate phase as the washing liquid.

22. The process of claim 23, wherein a gradual temperature gradient ismaintained through the extraction apparatus whereby the molal quantityof the solvent-free portion of the extract phase is maintainedsubstantially constant at least within the washing zone.

23. In an extraction process carried out by means of an extractionapparatus having extraction and washing zones and provided with meansfor introducing a solvent andal mixture to be extracted, and means forwithdrawing the ultimate raflinate and extract phases produced withinthe apparatus, the steps of introducing the solvent'and the mixture intothe apparatus, separately withdrawing said phases therefrom and chillingthe contents of the apparatus at the remote end of the washingzone at aneffective distance from the entrance of the mixture, thereby creating agradual change in temperature throughout at least the washing zone.

. WILLEM J. D. vAN DIJCK.

